One-month-old rats were fed 1 of 4 high-fat diets (20% fat) or chow (4.5% fat) for 3 months. Dietary saturated (SFA), monounsaturated (MUFA), or polyunsaturated (PUFA) fatty acids varied such that their independent effects on cognitive performance could be tested. Rats were tested on a variable-interval delayed-alternation task. Impairment in both the ability to learn the basic alternation rule and remembering trial-specific information over time was observed in rats fed the experimental diets relative to those fed chow. The degree of impairment was highly associated with the level of SFAs fed and independent of the MUFAs or PUFAs. Dietary fat altered brain phosphatidylcholine fatty-acid profile, but the membrane changes did not correlate with cognitive impairment. The results demonstrate that cognitive impairment is directly associated with SFA intake but suggest that the mechanism is independent of bulk brain membrane compositional changes.